My grandson has a 1999 Lincoln Town Car the gas gauge does not work right he says when he is driving it it dies on him when the gas gauge says it has a 1/2 tank of gas. I was driving it the other day and it did the same thing on me I put 10.00 in gas and it would not start. I had it jumped and it started right up. The gas gauge went down to empty then back up to a full tank then to a half tank to a 1/4 tank. What would cause this?